The humerus bone of the upper arm is part of a "ball and socket" joint at the shoulder. The proximal end of the humerus has an enlarged head or cortex that includes the "ball." The humeral shaft extends distally away from the proximal head toward the elbow joint.
Proximal humeral fractures are the most common humeral fractures. These are often found in patients who have fallen on their arms, creating an axial load on the humerus that causes a fracture of the humeral head. In a two-part fracture, The head or a single portion of the head is broken from the humeral shaft. Three- and four-part fractures involve the fracture of the humeral head into two or three fragments separate from the shaft. The nature of these fractures is generally predictable, as the head tends to fracture between the ball portion and one or both tubercles of the head to which ligaments attach. Proximal humeral fractures are particularly problematic in elderly, osteoporotic patients, and in those patients having cancerous tissue in the region of the fracture.
Existing treatments for multiple proximal humeral fractures may be unsatisfactory in many cases. Conventional techniques for wiring, suturing, or externally fixing fragments to each other and to the shaft are not entirely suitable for treatment of more complex fractures, or when tissues are weakened by disease. In these cases, surgical replacement of the shoulder joint may be required.
To avoid the more drastic measure of joint replacement, the present invention provides an elongated tapered nail or rod having an elongated body with a curved tapered shank that may be secured within a proximal portion of the humeral shaft, with a contiguous butt portion of the nail extending proximally from the shank to provide a solid foundation to which the humeral head fragments may be secured. The butt portion has transverse holes oriented at selected angles to receive fasteners attached to the fragments.
The curved tapered shape of the present invention permits it to be inserted into a cavity formed by a broach tool having the same shape as the nail, without significant interference or flexing of the bone or nail during insertion, and without broaching a too-large cavity having excessive clearance that would permit a loose fit between nail and bone. Also, the nail has a varying taper angle that creates a ridge positioned away from the distal tip, reducing stress concentrations on the bone that may occur at the tip of any reinforcing implant.